The invention relates to a method for laser remote processing of a workpiece on a fillet as well as a device therefor and in particular a method and a device for quality improvement for the remote laser welding of end fillet welds.
Laser remote processing is understood as a processing method which is carried out using the scanner technology or a scanner device. In this regard, a laser beam can be deflected by means of at least one movable mirror and positioned on or guided over the workpiece to be processed, so that very high processing speeds can be achieved. Furthermore the scanner device can have lens systems for focusing of the laser beam and/or further movable or fixed mirrors. The processing with the laser beam may be welding, melting or cutting.
Furthermore, the scanner device can be mounted on a movable mechanism. This may for example be a robot, a portal or the like, so that a movement of the scanner device along and/or around at least two axes is enabled. As a result, the working area of the laser remote system is increased. By simultaneous movement of the scanner device by means of the mechanism and movement of the laser beam by means of the scanner device a so-called “on the fly” processing can be implemented, so that the processing times are further reduced. However, the synchronization of movements, which is necessary in this case, brings with it certain requirements for precision of positioning. The requirement for precision of positioning is increased by the large working distance between the scanner device and the workpiece, which in laser remote systems usually amounts to at least 0.5 meter.
Thus, the requirements for precision of positioning described above result in variations between the desired course and the actual path of the laser on the workpiece. These variations are, in particular, critical when the workpiece is to be processed on a fillet.
In the vicinity of the fillet, the workpiece has a significant change in height. If the laser beam deviates from a predetermined position, then the laser beam can no longer be correctly focused on the workpiece. If the processing is welding, such as for example the formation of a fillet weld in the fillet, then faulty positioning leads to welding errors. In particular, in the welding of two metal sheets positioned in a lap joint for formation of an end fillet weld, positioning on the upper metal sheet leads to defective penetration welding and considerable spatter due to lack of zinc degassing. Likewise, positioning on the lower sheet leads to holes. Furthermore, the quality of the seam drops when a predetermined gap width is not maintained, since the connection width of the weld seam is reduced.
Thus, the object of the present invention is to provide a method for remote laser processing of a workpiece on a fillet as well as a device for carrying out the method, by which the process stability and process quality can be improved.
This object is achieved by a method and a device according to the invention with the features set forth in the independent claims.
In the method according to the invention, the working range of the laser beam on the workpiece is illuminated by illuminating radiation and is detected by at least a first image capturing unit. The captured image data are automatically evaluated and, if appropriate, an automatic correction of the path of the laser beam is carried out on the basis of the evaluation.
The workpiece may be a single component. Alternatively, the workpiece may also consist of two or more components. Metal shaped bodies, such as for example metal profiles, can be used as components. The components may also, for example, be metal sheets, which may be flat metal sheets or three-dimensional shaped metal sheets. These are preferably steel sheets. These may be for example zinc- or aluminum-coated steel sheets which are provided with an anti-corrosion coating based on zinc or aluminum.
Fastening elements, which may for example be cylindrical or in the form of spherical segments, can be fastened on the metal sheets.
A workpiece region in which two adjacent surfaces are inclined at an angle of less than 180° relative to one another is designated as a fillet. The fillet may be designed as an edge, alternatively the fillet may be formed in dish shape between the two surfaces, i.e. the delimiting surfaces merge into one another with a radius in the region of the fillet. The fillet may be formed for example by two adjacent straight areas which are disposed as a lap joint, T joint or angle joint, or for example by a surface which is cylindrical or in the form of spherical segments, which is disposed adjacent to a straight surface. The two areas delimiting the fillet can adjoin one another, but also there may be a gap between the two areas. The fillet may be constructed on a component, for example the component may be L-shaped or a web may project from the component. Alternatively, the fillet can also be formed by a corresponding arrangement of two components. For example, two components can be disposed partially overlapping, so that the fillet is produced for example between the end face of the upper component and the surface of the lower component. Likewise, the fillet can also be formed by two components which are disposed one above the other and partially penetrate one another.
The method according to the invention uses optical monitoring of the working range of the laser, wherein both data regarding the actual position of the laser beam on the workpiece and also data on the position of the fillet are evaluated.
In this case, a range which encompasses both the process zone and the process advance zone is designated as the working range of the laser. In this case the keyhole, i.e. the immediate impact zone of the laser beam, and the adjacent melting zone are designated as the process zone. The process advance zone is located before the melting zone in the processing direction. The immediate process advance zone designates the area which is located less than 2 mm before the melting zone in the processing direction.
The illuminating radiation may be visible light, alternatively UV or infrared radiation can be used. In one embodiment, the illuminating radiation is coupled into the beam path of the processing laser beam and is guided coaxially with respect thereto on the workpiece. In this regard, an additional optical unit and/or mirror can be provided in the scanner device. By way of example, the illuminating radiation and the processing laser beam are simultaneously directed onto the workpiece. In a further embodiment the illuminating radiation can be guided over the workpiece by a second scanner device, i.e. a scanner device other than the one used for the processing laser beam. The illuminating radiation is preferably directed radiation, for example it may be laser radiation. The wavelength of the illuminating radiation is preferably different from the wavelength of the laser beam for processing.
The working range of the (processing) laser beam is located in the field of view of at least a first image capturing unit. In one embodiment, the working range is located in the field of view of a first and a second image capturing unit. The first or second image capturing unit may, for example, have one or more sensors or cameras and may optionally comprise a computer unit. The image capturing unit captures images from the working range of the laser. The capture preferably takes place during the processing. The image capturing unit captures a part of the illuminating radiation which is reflected from the working range of the workpiece. Furthermore the image capturing unit may capture process light. The process light is composed of radiation which is reflected by the processing site and of secondary radiation which, during the processing, results from an interaction between the workpiece and the laser beam.
The recorded image data can be evaluated automatically. The evaluation of the image data takes place, for example, taking into account the illumination data and/or the output data of the processing laser using an image processing algorithm. An evaluation takes place, for example, with regard to the position of the fillet and with regard to the actual position of the processing laser beam. According to the results of the evaluation, the path of the laser beam is adapted for processing in order to correspond as closely as possible to the desired path.
According to the invention, the illuminating radiation is directed onto the workpiece at an angle of attack which is set as a function of the fillet geometry of the workpiece. In this case, the angle of attack is the lateral angle of attack, that is to say the inclination of the beam transversely with respect to the processing direction or weld seam. The angle of attack designates the angle at which the laser beam is inclined relative to the vertical onto the surface of the workpiece facing the scanner device. It has been shown that a reliable and precise edge recognition can also be ensured for difficult fillet geometries by the choice of an angle of attack which is dependent upon the geometry of the fillet. In particular, the angle of attack is set depending upon the fillet angle, i.e. the angle enclosed by the two areas delimiting the fillet. Thus, the process stability is considerably improved by a simple measure. The fillet angle can be determined, for example, by a measurement on the component before the start of processing. Thus, the method is suitable in particular for the processing of sheared metal sheets, for which a shearing angle of approximately 90° frequently cannot be ensured or which have phases or flash on the end face.
In one embodiment, the illuminating radiation which is reflected out of the immediate process advance zone is evaluated in order to determine the location of the fillet or of the edge configuration. In this way, a match can be determined between the actual position of the laser beam and the further edge configuration or fillet configuration. Thus, the quality of the beam correction can be improved by comparison with a determination of the edge configuration at the level of the processing laser.
In a further configuration, the edge recognition takes place in that a second scanner device with a second image capturing unit is directed onto a following processing site. The following processing site may, for example, be a few millimeters or a few centimeters away from the current processing site, i.e. before the processing site in the processing direction. Thus, at the following joining point the actual edge position can already be recognized and fed back to the controller as an adjustment value, whilst the processing is still taking place on the previous processing site.
The evaluation of the image data takes place preferably by determination of a grey scale value. For the data from the process advance zone, for example, the distribution of the grey scale values transversely with respect to the processing direction gives information regarding the component geometry. For example, the position of the fillet or of the edge can be determined from a maximum or minimum of the grey scale values. By a further comparison with the current position of the laser, the further path of the laser can be adapted to the configuration of the fillet and faulty positioning can be avoided in the future.
Further process reliability can be obtained in that the image data with regard to the contrast are evaluated. Increased soiling of the protective glass which protects the image capturing unit against soiling by process gases, such as for example welding fume and spray, is accompanied by a decrease in the contrast of the capture images. The monitoring of a sufficient contrast can prevent the failure of the edge detection in that, for example, when a predetermined threshold value is reached, a signal is emitted to replace the protective glass.
Because of the increase in the process reliability described above with regard to the edge or fillet recognition, the method is suitable in particular for the formation of a fillet weld in the fillet. The fillet weld may be produced as a continuous seam or with interruptions of the seam.
Moreover, ideal degassing conditions are produced by the provision of a fillet weld, and for this reason the method is suitable in particular for connecting to one another two metal sheets disposed in a lap joint by means of an end fillet weld, i.e. a seam between the end face of one metal sheet and the adjacent contact surface of the other metal sheet. Preferably, the metal sheets can be connected without a gap (so-called zero gap). The method is suitable in particular for the welding of metal sheets which have a coating comprising zinc or aluminum. Thus, the method is also suitable for mass production in vehicle bodywork construction.
In a further embodiment, the image data are evaluated in order to determine a gap dimension on the fillet and optionally to correct the position of the laser beam. In this way it is possible in a simple but effective manner to prevent the occurrence of welding errors (for example due to a reduced connection width) due to variations in the gap dimension and resulting in a reduction in the process reliability or quality. Thus, variations in the gap dimensions, which cannot be completely prevented because of component tolerances or faulty clamping of the components, can be compensated for by appropriate adaptation of the path or the focus of the laser beam. For example, by beam oscillation more material can be melted for the joint.
The determination of the gap dimension can, for example, be obtained from the grey scale values of the image data. Thus, a gap in the grey scale representation appears for example as a dark region between two light regions. A conclusion as to the gap width can be drawn from the width of the region. The control device carries out corresponding changes to the beam guiding, for example, changing the position or the focus location.
In a further embodiment, the process reliability is further improved in that additionally the process light is evaluated in order to recognize remediable processing errors. Because of faulty positioning of the laser relative to the fillet, an incorrect processing result may be produced, but can still be remedied. For example, in the case of a fillet seam weld on the lap joint, the laser beam can only be positioned on the upper sheet. The resulting lack of penetration welding can be recognized in the process light, for example, by the fact that in the grey scale representation no black spot can be seen in the process light. However, such a process error can still be corrected, which in the present method can advantageously be carried out immediately after the evaluation in the processing method. In this case, the control device carries out a corresponding correction of the path of the laser beam in order to direct the laser beam, for example, again over an incorrect portion of the path.
Furthermore, the process reliability can be improved in that the image data from the process zone are evaluated in order to recognize errors which can no longer be remedied and if appropriate to generate an error signal. Such errors may occur, for example, if holes have been produced in the workpiece due to faulty positioning. For example, the formation of holes is associated with a collapse of the keyhole and consequently can be recognized by the absence of the process light. An error signal may be emitted, for example, in the form of an electrical signal, resulting in interruption of the processing operation, for example. Alternatively, the error signal may also be an identification of the workpiece by, for example, a marking. For example, the control device may be configured in order to generate the error signal or to adjust and direct the laser beam on the tool for application of the identification. With the aid of the error signal the workpiece can be discarded without a renewed inspection being necessary.
By the use of a second scanner device comprising a second image capturing unit and a second illumination device, an improved quality recognition can be achieved. For example, a greater flexibility in the irradiation of the relevant location, such as for example the weld seam, is possible. As a result, the reliable evaluation of the weld seam is ensured.
For the described evaluations suitable evaluation algorithms are used which are known from the prior art.
The method described above for seam tracking, in combination with the various evaluations described, ensures a process reliability for the laser remote processing of a component with a fillet, in particular for a fillet seam weld, which achieves the necessary dimension for industrial use.
In a further embodiment, an additional processing laser beam is guided over the workpiece. The additional processing laser beam is preferably guided over the structural part by means of a scanner device other than the one guiding the processing laser beam, for example, by means of the second scanner device. This enables seam preparation and/or seam reworking.
The additional processing beam can also be guided coaxially with respect to the processing beam in order to increase the process stability.
In one embodiment, the additional processing laser beam is subsequently positioned on the location processed by the processing laser, for example the welded seam, so that for example a subsequent seam smoothing can be achieved.
Furthermore, in one embodiment the additional processing laser beam can be used for advance component preparation, such as for example for preheating, zinc removal or cleaning, by positioning on the edge/joint position which is not yet welded.
If, with the method, an end fillet weld is to be formed between an end face of an upper metal sheet and an adjacent contact surface of a lower metal sheet, then the regulation of the seam tracking can be further improved in that the upper metal sheet has, on its surface facing away from the lower metal sheet, a convex portion which adjoins the end face. At least a part of the convex portion faces in the direction of the scanner device, so that the reflection of the illuminating light is improved and the edge or fillet recognition can be increased. A corresponding shaping on the upper sheet can be achieved, for example, by a corresponding shaping on the pressing tools to produce the sheet blank.
The device according to the invention for laser remote processing of a component on a fillet comprises at least a first scanner device and at least one laser source, of which the laser beam can be directed over the workpiece by means of the first scanner device. A solid state laser is preferably used as the laser source, but alternatively gas or dye lasers can be used. The laser source preferably generates, for example, a laser beam with a wavelength of more than 1000 nanometers.
Furthermore, the device according to the invention has an illumination device from which the beam of light strikes the workpiece at an angle of attack, wherein the angle of attack is dependent upon a fillet geometry of the workpiece. The illumination device may be a light source which generates light in the visible frequency spectrum or UV or infrared light, for example a laser source. The illumination device preferably generates a directed radiation. The illumination device may preferably be a laser source. For example, it may be a laser source which generates a laser beam with a wavelength of more than 800 nanometers. The illumination device may be mounted on the scanner device or installed therein. Alternatively, the illumination device may be mounted on a second scanner device. The illumination device is preferably mounted so that the illuminating radiation is coupled into the beam path of the processing laser beam and can be directed coaxially with respect thereto by the movable mirror of the scanner device. The adjustment of the angle of attack of the illuminating radiation can take place, for example, by means of movable mirrors, such as for example the movable mirror of the scanner device. If the illuminating radiation is coupled into the beam path of the processing laser, the adjustment of the angle of attack preferably also takes place by means of the same mirror by which the processing laser beam is guided over the workpiece.
Furthermore, the device according to the invention has at least one image capturing unit, as described above, which captures image data from the processing region of the laser beam as well as a control device which, if need be, corrects the path of the (processing) laser beam with the aid of an evaluation of the captured image data.
The evaluation can be carried out by the at least one image capturing unit. Alternatively, the evaluation can also be carried out by the control device. The image capturing unit or the control device are configured appropriately for evaluation, for example they can include an evaluation unit, such as for example a microcontroller.
In order to be able to adjust or reset the path of the laser beam and the setting of the angle of attack of the illuminating radiation, the control device is appropriately configured and, for example, is connected via interfaces to the image capturing unit, the scanner device, the laser source for generation of the processing laser beam and the illumination source.
In one embodiment, the scanner device is mounted on a movable mechanism, such as for example a robot or a portal, so that laser processing “on the fly” is possible. In this case the control device is configured in order to synchronize and to control the necessary synchronization between the movements the movable mechanism and of the laser scanner.
If the method described above is carried out by the device according to the invention, then the same advantages and technical effects described there are achieved.
In one embodiment, the device has a second scanner device. This is mounted for example on the first scanner device. By means of control engineering the second scanner device can be incorporated into the control of the first scanner device, for example as additional axes. Alternatively the second scanner device can have a dedicated control.
Furthermore, the device can have an additional processing laser which can preferably be directed onto the component by means of the second scanner device. The additional processing laser may for example be a solid state laser or also a gas or dye laser. A diode laser is preferably used.
Furthermore, the device may have a second image capture device which is mounted on the second scanner device. The image capture device is preferably disposed coaxially with respect to the beam path of the additional processing laser.
Furthermore, a second illumination device can be provided on the second scanner device. The light from the second illumination device is guided by the second scanner device preferably coaxially with respect to the beam path of the additional processing laser.
Advantageous embodiments of the invention are disclosed by the subordinate claims and the embodiments.
The characteristics, features and advantages of this invention which are described above as well as the way in which these are achieved can be understood more clearly in connection with the following description of the embodiments. In so far as the expression “can” is used in this application, this relates both to the technical possibility and to the actual technical implementation.
Embodiments are explained below with reference to the appended drawings.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.